A hydrogenated block copolymer of a conjugated diene monomer and a vinyl aromatic monomer has elasticity equivalent to that of vulcanized natural rubber or synthetic rubber at ordinary temperature, although it is not vulcanized. Such a hydrogenated block copolymer is excellent in weathering resistance and heat resistance, and further, it has processability equivalent to that of a thermoplastic resin at a high temperature. Hence, the hydrogenated block copolymer has been put to a wide range of practical uses for appliance parts, automobile parts, wire-coating materials, industrial parts, adhesive materials, wrapping materials, medical devices, etc.
A polypropylene resin composition, which is obtained by mixing a polypropylene resin with a hydrogenated block copolymer having a block of a relatively low content of vinyl aromatic monomer and a block of a conjugated diene monomer with a relatively high vinyl bond content, is a material excellent in transparency and flexibility. Thus, the polypropylene resin compositions have been widely used for medical use, coating materials, wrapping materials, toys, etc., with intended uses for situations in which transparency can be utilized.
In recent years, studies regarding alternative materials for soft vinyl chloride resins have been conducted. As an alternative material having flexibility, a composition comprising a hydrogenated block copolymer obtained by hydrogenation of a copolymer having a block of a vinyl aromatic monomer and a block in which the vinyl bond content of a conjugated diene monomer portion is 62% or more, and a polypropylene resin, has been disclosed (see, for example, Patent Literature 1).
Moreover, there has been disclosed a method for producing, at a high production rate, a hydrogenated block copolymer which has a conjugated diene monomer with a high vinyl bond content and a vinyl aromatic monomer block with a narrow molecular weight distribution, and which has a narrow molecular weight distribution (see, for example, Patent Literature 2).
Furthermore, there has been disclosed a thermoplastic elastomer pellet, which is formed by adding fine particles of polypropylene having an average particle diameter of 150 μm or less to a pellet of a thermoplastic elastomer composition obtained by the melt mixing of a hydrogenated styrene elastomer, a softener for rubber and polypropylene (see, for example, Patent Literature 3).